Process for acid copper plating of steel

ABSTRACT

A PROCESS FOR THE COPPER ELECTROPLATING OF STEEL, PARTICULARLY COMPLEX STEEL PARTS HAVING RECESSED AREAS, WHEREIN A DISPLACEMENT NICKEL OR COBALT-NICKEL DEPOSIT IS FORMED ON THE STEEL SURFACE BY TREATMENT WITH AN IMMERSION NICKEL OR COBALT-NICKEL PLATING BATH AND, THEREAFTER, THE THUSPLATED SURFACE IS ELECTROPLATED WITH COPPER FROM AN ACID COPPER ELECTROPLATING BATH.

United States Patent US. Cl. 204-38 B 7 Claims ABSTRACT OF THE DISCLOSURE A process for the copper electroplating of steel, particularly complex steel parts having recessed areas, wherein a displacement nickel or cobalt-nickel deposit is formed on the steel surface by treatment with an immersion nickel or cobalt-nickel plating bath and, thereafter, the thusplated surface is electroplated with copper from an acid copper electroplating bath.

This is a continuation-in-part of our copending application Ser. No. 834,861, filed June 19, 1969, now abancloned.

This invention relates to a method for the copper plating of steel surfaces and more particularly it relates to an improved process for the copper electroplating of complex steel parts having recessed areas.

Acid copper electroplating baths have long been used in industry, particularly in the decorative field as an undercoat for nickel-chromium deposits. With the development in recent years of processes which will produce a fully bright, ductile, high leveling copper deposit, there has been even wider use of acid copper plating solutions. With such solutions, it is now possible to process large steel components from the leveling acid copper solutions directly to nickel and chromium plating baths, without the necessity for buffing the copper deposit prior to the application of the nickel and chromium. In addition to the savings resulting from the reductions in polishing or bufiing costs, it has further been found that these copper deposits contribute to the durability of decorative coatings, thus making it possible to substitute copper for a portion of the nickel plating with micro-porous or microcracked chromium, without loss of durability.

Although these acid copper plating solutions offer many advantages, they are subject to one major difiiculty which has limited their even greater use. This difficulty is their inherent tendency to deposit a loosely adherent displacement or immersion deposit on steel surfaces which are treated therewith. Although in some instances, this difiiculty can be overcome by applying an electroplated strike of copper or nickel, where complex steel parts are treated, particularly those having recessed areas, the strike deposit will not be sufiiciently thick to retard attack by the acid copper solution, or may not be present at all. There is, therefore, a deposition in such areas, of a non-adherent copper deposit which is easily dislodged when the part is subjected to some movement, as in rise tanks or agitated nickel plating solutions. When this occurs, the effects in the nickel deposit are roughness and pitting. It is because of this difficulty that the use and application of these acid copper plating solutions has been limited to the plating of relatively simple shapes which permit complete and adequate coverage by the electrodeposition of the copper or nickel strike preceding the electrodeposition from the acid copper solution.

It is, therefore, an object of the present invention to provide an improved process for the electrodeposition of acid copper plating solutions which permits the use of such solutions on complex steel parts.

3,589,380 Patented Sept. 5, 1972 A further object of the present invention is to provide an improved process for forming an adherent deposit from an acid copper plating solution even in recessed areas of complex steel parts.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

Pursuant to the above objects, the present invention includes a process for the copper electroplating of steel which comprises treating a steel surface with an immersion nickel or cobalt-nickel plating bath, forming a displacement nickel or cobalt-nickel deposit on the steel surface and, thereafter, electrodepositing copper on the thustreated surface from an aqueous acidic copper electroplating bath. In this manner, an adherent copper plate is obtained from the acid copper plating bath over the entire steel surface being treated, even in those areas, such as recesses, which receive little or no electrical current.

More specifically, in the practice of the method of the present invention, the steel surface is desirably cleaned, using various conventional cleaning techniques, prior to treatment with the plating solutions of the present invention. As are known to those in the art, such cleaning techniques may utilize alkaline, acidic, or organic solvent cleaning compositions, and may include spraying, scrubbing, vapor degreasing, ultrasonic cleaning, steam cleaning, and the like. Once the cleaning and/or other surface preparation of the steel surface has been completed, the surface may then be treated with the immersion nickel plating bath.

Desirably, however, following the cleaning or other pretreatment of the steel surfaces, an electrolytic nickel, cobalt, cobalt-nickel or copper strike is applied to the surface. Where a copper strike is applied, the various conventional copper strike plating baths, such as the copper cyanide baths, may be used. Such baths generally contain copper cyanide, an alkali metal cyanide, and an alkali metal hydroxide. Additionally, such baths may also contain Rochelle salts or other addition agent which may aid in the operation of the bath by modifying the structure of the deposits, retarding carbonate buildup in the bath or assisting in anode corrosion. The operation of such cop per strike baths is conventional and well known to those in the art. Typically, these baths are operated at temperatures of from about room temperature up to about 70 degrees C. for plating times of from about V2 to 2 minutes at a tank voltage of from about 4 to 6 volts.

Where a nickel, cobalt, or cobalt-nickel strike is applied, as with the copper strike, various conventional nickel and/or cobalt containing strike electroplating baths may be used. Typically, such baths may contain various nickel and/ or cobalt salts, such as sulfates, and chlorides, as well as boric acid, and the like, and are exemplified by Watts baths in which the nickel chloride is present in amounts up to about grams/liter. As with the copper strike baths, the operation of such strike solutions is conventional and well known to those in the art. In addition to the conventional nickel and/or cobalt containing strike electroplating baths, however, if desired, the strike plating bath used may be the immersion nickel or cobalt-nickel plating bath which is also used to form the displacement nickel or cobalt-nickel deposit on the surface. In such instances, the steel surface will be contacted with the immersion plating bath and the nickel and/or cobalt containing strike plate will be electrodeposited from this bath on the steel surface. In this manner, the operation of the present process may be simplified in that only a single plating solution will be necessary in order to obtain both the electro strike plate and the displacement nickel deposit.

The displacement nickel or cobalt-nickel deposit is formed on the steel surface by treatment with an immersion nickel or cobalt-nickel plating bath. Various immersion nickel or cobalt-nickel plating baths may be used which will form a displacement nickel or cobalt-nickel deposit having a thickness of at least three millionths of an inch on the steel surface in a contact time with the steel surface of no more than about five minutes. This is not to say, however, that in some instances the immersion plating solution may not be in contact with the steel surface for periods greater than five minutes, but, rather, that in order for the immersion plating solution to be effective in the process of the present invention, the rate at which a coating is obtained from it must be sufficient that after five minutes of contact with the steel surface, the deposit is at least three millionths of an inch thick.

Desirably, immersion nickel baths are used, which baths are aqueous solutions having a pH of from about 2.0 to 4.5 and containing from about 100 to 600 grams per liter of NiCl .6H O, up to about 150 grams per liter NaCl and up to about 50 grams per liter H BO Preferably, the immersion nickel plating baths used will contain from about 300 to 600 grams per liter of the nickel chloride, from about 75 to 150 grams per liter of the sodium chloride, and up to about 30 grams per liter of the boric acid. In some instances, it has also been found to be desirable to include in the immersion nickel plating bath a suitable wetting agent, desirably an anionic wetting agent. Such wetting agents are desirably present in amounts up to about 1 gram per liter, with the alkyl aryl sulfonates and sulfonic acids, such as nonyl benzene sulfonic acid being exemplary of preferred wetting agents which may be used. Additionally, where the immersion nickel plating bath is also used as the electro strike plating bath, it may also desirably contain one or more additives which will be effective in ductilizing and/ or grain refining of the electroplate which is produced. Suitable additives which may be used, without detrimental effect on the displacement nickel coating which is formed by the bath, are the various sulfo oxygen compounds such as saccharine, etc., as are known to those in the art.

Alternatively, however, the immersion plating bath used may be a cobalt-nickel bath in which up to about 95% by weight of the nickel salts in the immersion nickel bath has been replaced with cobalt salts. Such baths are similar to the immersion nickel baths described hereinabove, except for the replacement of the nickel by cobalt. It has been found that although with a separate strike bath, this strike bath may be all cobalt, this is not the case with the immersion plating bath. These baths must contain at least about by Weight nickel, calculated as NiCl .6H O, to produce acceptable results. Additionally, of course, they may contain the same additives and may be used in the same manner as the immersion nickel baths.

Where a separate copper or nickel and/or cobalt containing strike electroplate is used, following the formation of the desired strike plating plate, the steel surface is contacted with the immersion nickel or cobalt-nickel plating bath, preferably by immersing the steel surface in the plating solution. Desirably, this immersion plating solution is at an elevated temperature, temperatures within the range of about 60 to 80 degrees centigrade being typical, with contact times of from about 3 to 5 minutes. It is to be appreciated, however, that in some instances, depending upon the specific operating conditions used, temperatures and times which are outside of these ranges may also be utilized to produce satisfactory results. During the application of the displacement nickel or cobalt-nickel plate, the plating bath may be still or, if desired, may be agitated, with air agitation being preferred where agitation is used.

Where the immersion plating solution is also used as the strike electroplating solution, the steel surface to be treated is contacted with the plating bath and the bath is electrolyzed so as to electroplate the nickel or cobalt-nickel strike on the steel surface. The conditions under which this electroplating is effected are those which are conventionally used for the application of a nickel strike, plating times of from about 1 to 4 minutes at current densities of from about 20 to 45 amperes/ square foot being typical. Following the application of the desired nickel or cobalt nickel strike plate on the steel surface, the passage of current through the plating bath is then discontinued and the steel surface is retained in the bath for a period sufiicient to effect the formation of the desired displacement nickel or cobalt-nickel coating on at least those portions of the steel surface which have received little or no strike plate. Generally, the conditions for effecting the formation of this displacement coating will be substantially the same as those which have been set forth hereinabove for the use of this plating solution as an immersion bath, i.e., temperatures of from about 60 to degrees centigrade and immersion times of from about 3 to 5 minutes.

It is to be appreciated that in many instances, when using the immersion nickel or cobalt-nickel plating bath for the application of the strike plate, particularly where the steel surface being treated has recesses or similar areas in which there is little or no electrical current, the displacement coating will be formed on these portions of the surface during the time of the electrolytic deposition of the strike. In such instances, the deposition of the displacement coating in these areas of low or no current density, will be sufi'icient to provide the necessary protection of these areas, without the necessity for the application of the displacement coating as a separate step. Accordingly, it is to be understood that the method of the present invention also includes this operation of the process wherein there is a simultaneous deposition of the displacement nickel or cobalt-nickel coating at the time of the electrolytic deposition of the strike. It has been found, however, that satisfactory protection by means of this simultaneous deposition may not always be obtained on all types of steel surfaces. Accordingly, in the preferred manner of operation for the process of the present invention, the displacement nickel or cobalt-nickel deposit from the immersion nickel or cobalt-nickel plating solution is carried out as a separate step, following the application of the electro strike coating, in order to insure adequate protection of the steel surface.

Following the application of the displacement coating the steel surface is then electroplated, using an acid copper plating bath. If desired, prior to the application of the acid copper plate, the metal surface may be rinsed with water and/or with a dilute aqueous acidic solution, such as H 50 NaHSO HBF and the like. The use of a dilute sulfuric acid rinse, e.g. an aqueous solution containing about 10-15% by weight H 50 has been found to be particularly deirable Where a separate electrolytic nickel and/or cobalt containing strike has been applied to the surface. In such instances, it is found that the sulfurio acid rin'se serves to reactivate the nickel and/ or cobalt containing strike which may have become somewhat passivated as a result of the subsequent treatment with the immersion nickel or cobalt-nickel plating bath. Typically, the rinsing with this sulfuric acid solution may be carried out for periods of up to about 1 minute, using solution temperatures up to about 50 degrees C.

Various acidic copper electroplating baths, as are known to those in the art, may be used for the application of the copper electroplate in the method of the present invention. Typically, such acid copper electroplating baths are aqueous acidic solutions of copper sulfate, copper fiuoborate, copper nitrate, copper sulfamate, the copper alkyl sulfonates and disulfonate's, and the like. General 1y, such acid copper plating baths will also contain one or more additives which are effective in improving the lustre, leveling, ductility, etc. of the copper electroplate obtained. Typical of such acid copper electroplating baths and the additives which they may contain are the plating baths described in US. Pats. 2,707,166; 3,267,010; and 3,288,690. It is to be appreciated, of course, that other acid copper electroplating baths, other than those specifically set forth may also be used to effect the desired copper plating the surfaces.

The copper plate is applied to the steel surfaces by the electrolysis of the acid copper electroplating baths in the conventional manner as is known to those in the art. Generally, such baths will be operated so as to produce a copper plate having a thickness of from about 0.0002 to 0.0015 inch, typical operating conditions to produce such a plate including bath temperatures of from about 18 degrees to 60 degrees C., average current densities from about 15 to 300 amperes/ sq. ft. and plating times of from about 10 to 40 minutes.

It is found that although the displacement nickel or cobalt-nickel coating produced by the treatment of the steel surfaces with the immersion nickel or cobalt-nickel plating solution is extremely porous, so that the acid copper electroplating solution attacks the steel or iron exposed in the pores and deposits copper therein, surprisingly, this reaction is apparently self limiting as the thickness of copper remains relatively low even after lengthly exposure times in the acid copper electroplating solution. Apparently, the pores are sealed so that subsequent diffusion of the acid copper electroplating solution and attack on the steel does not readily occur. This is in contrast to the attack of acid copper electroplating solutions on uncoated steel which results in the formation of the loosely adherent copper coating on the steel. Thus, by the method of the present invention, an adherent, copper plate is formed on the steel surfaces treated, even where such surfaces have recesses or similar areas of little or no current density during the electroplating process. By means of the method of the present invention, the areas in which bright acid copper electroplating solutions can be successfully used are greatly extended so that the advantages resulting from the use of such plating solutions can now be realized even in the plating of complicated and complex steel surfaces.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. In these examples, unless otherwise indicated, parts and percent are by weight and temperatures are in degrees centigrade.

EXAMPLE 1 Clean steel tubing is given an electro nickel strike plate using a Watts bath containing 299 grams per liter nickel sulfate, 42 grams per liter nickel chloride and 44 grams per liter of boric acid. The bath was operated at a pH of about 3.6, at temperatures of about 60 degrees C., using a current density of about 30 amps per square foot. Following the application of the nickel strike, the steel tubing was immersed in an immersion nickel plating bath containing 314 grams per liter NiCl -6H O, 76 grams per liter NaCl and 23.2 grams per liter H BO for a period of minutes. The immersion nickel plaitng bath had a pH of about 4.0 and was at a temperature of about 70 degrees centigrade. Following the treatment with the immersion nickel plating bath, the steel tubes were rinsed, then immersed for 30 seconds in an aqueous sulfuric acid solution containing about 15% by weight H 50 which sulfuric acid rinse was at a temperature of about 40 degrees C. Following rinsing, the steel tubing was then electroplated using an aqueous acid copper electroplating bath which contained 236 g./l. CuSO -5H O and 52 g./l. H 80 The bath was operated at a temperature of 27 degrees C., a current density of about 40 amps/ square foot to produce a copper electroplate on the steel tubing having a thickness of about 0.0005 inch. It was found that an excellent, adherent copper coating was obtained even on the interior surfaces of the steel tubing.

EXAMPLE 2 By way of comparison, the procedure of Example 1 was repeated with the exception that the treatment of the steel tubing with the immersion nickel plating solution to produce a displacement nickel coating thereon was omitted and the copper plating from the acid copper plating bath was effected directly on the nickel strike. In this instance, although a good, adherent copper plate was obtained on The copper strike was applied using a bath temperature of 57 degrees C., a plating time of 2 minutes, and a current density of 25 amps/square foot. Using this procedure, plating results comparable to those in Example 1 were obtained.

EXAMPLE 4 The procedure of Example 1 was repeated with the exception that the immersion nickel plating bath was substituted for the Watts nickel bath and the nickel strike plate was obtained by electrolyzing the immersion nickel bath for a period of 2 minutes, using a current density of 40 amps/square foot. Thereafter, the electric current was discontinued and the steel tubing was permitted to remain in the nonelectrolyzed immersion nickel bath for the period given in Example 1. Using this procedure, the plating results obtained were comparable to those in Example 1.

EXAMPLE 5 A solution was formulated containing 595 grams/liter NiCl .6H *O and 32 grams/liter H BO Using this solution at a pH of 3.6, steel tubes were electrolyzed for 4 minutes at a current density of 30 amps/square foot. In this manner, there was obtained a nickel strike electroplate on the exterior of the tubes and a simultaneous displacement nickel deposition on the tube interiors, which plating results were comparable to those obtained in Example 1.

EXAMPLE 6 An aqueous immersion nickel plating bath was formulated containing 559 grams per liter NiCl .6H O and 29.5 grams per liter H -BO which bath had a pH of 4.0. Low carbon steel panels were immersed in this nickel solution for varying periods of time at differing bath temperatures and the thickness of the displacement nickel deposit obtained was measured. Using this procedure, the following results were obtained:

Plate thickness (millionths of an inch) 7 EXAMPLE 7 The procedure of Example -6 was repeated with the exception that the temperature of the immersion nickel plating bath was maintained constant at about 68 degrees C. and the pH of the bath was varied. Using this procedure, the following results were obtained:

Plate Immersion thickness time (millionths pH (minutes) of an inch) EXAMPLE 8 The procedure of Example 6 was repeated with the exception that the temperature of the immersion nickel plating bath was maintained constant at about 68 degrees C. and the pH was maintained constant at about 4.0 while the nickel chloride content of the bath was varied. Using this procedure, the following results were obtained:

Plate The procedure of Example 5 was repeated with the exception that the solution used contained 540 grams/liter CoCl .6H O, '60 grams/liter NiCI ASH O and 30 grams/ liter H BO and had a pH of 3.8. Steel bicycle seat riser posts were plated by electrolyzing this solution for 3 minutes at a current density of -30 amps/square foot and a solution temperature of 7174 C. In this manner, there was obtained a nickel-cobalt strike electroplate on the exterior of the posts and a simultaneous displacement nickel-cobalt deposition on the interior of the posts, which plating results were comparable to those obtained in Example 1.

EXAMPLE 10 The procedure of Example 1 was repeated with the exception that the immersion plating bath used contained 360 grams/ liter CoCl .6H O and 240 grams/liter NiCl .6H O

and comparable results were obtained.

While there have been described various embodiments of the present invention, it is to be appreciated that these specific embodiments are intended merely to be exemplary of the preferred manner in which the invention, as described by the following claims, may be practiced.

We claim:

1. A process for the copper electroplating of steel which is comprised of steel surfaces which receive little or no electrical current in an electroplating process which comprises treating a steel surface with an immersion nickel or cobalt-nickel plating bath, wherein the immer sion plating bath contains at least about 5% by weight nickel, calculated as NiCl -6H O, forming a displacement nickel or cobalt-nickel deposit on the steel surface and, thereafter, electrodepositing copper on the thus-treated surface from an aqueous acidic copper electroplating bath.

2. The process as claimed in claim 1 wherein a nickel, cobalt, cobalt-nickel, or copper strike electroplate is also applied to the steel surface prior to treatment in the immersion nickel or cobalt-nickel bath.

3. The process as claimed in claim 2 wherein the strike is a nickel or cobalt-nickel strike which is applied by electrolyzing the immersion plating bath and thereafter, the electric current is discontinued and the steel surface is maintained in the immersion plating bath for a period sufficient to form the desired displacement nickel or cobalt-nickel coating on the uncoated steel surface.

4. The process as claimed in claim 2 wherein prior to the application of the copper electroplate, the treated steel surface is rinsed with an acidic solution to reactivate the strike electroplate.

5. The process as claimed in claim 1 wherein the immersion plating bath is an aqueous solution comprising from about to 600 grams per liter NiCl -6H O, up to about grams per liter NaCl and up to about 50 grams per liter H BO 6. The process as claimed in claim 5 wherein the immersion plating bath is an aqueous solution comprising from about 300 to 600 grams per liter of the nickel chloride, from about 75 to 150 grams per liter of the sodium chloride and up to about 30 grams per liter of boric acid.

7. The process as claimed in claim 1 wherein a nickel or cobalt-nickel strike is applied by electrolyzing the immersion plating bath and wherein the displacement nickel or cobalt-nickel coating is deposited substantially simultaneously during the electrolysis on at least the low current density portions of the steel surface.

References Cited UNITED STATES PATENTS 3,546,080 12/ 1970 Iannone 204-40 3,485,725 12/ 1969 Koretzky 204-38 R 3,264,199 '8/1966 Fassell et al 204-38 R 3,243,361 3/1966 Clark 204-38 R 3,206,324 9/1965 Daesen 106-1 2,878,172 3/1959 Scavullo 204-40 2,835,630 5/1958 Huddle et al. 204-38B 2,776,255 1/ 1957 Hammond et al. 204-40 FOREIGN PATENTS 493,518 12/ 1937 Great Britain 204-40 GERALD L. KAPLAN, Primary Examiner R. L. ANDREWS, Assistant Examiner U.S. Cl. X.R. 

